Oxygen scavenger and boiler water treatment chemical

ABSTRACT

A boiler water treatment chemical includes a heterocyclic compound with N-substituted amino group, or the salt thereof, and alkaline agent and/or water soluble polymer.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is a divisional patent application of U.S. patentapplication Ser. No. 09/404,202 filed on Sep. 23, 1999, which is adivisional patent application of U.S. patent application Ser. No.08/975,000 filed on Nov. 20, 1997.

FIELD OF THE INVENTION AND RELATED ART

[0002] The present invention relates to an oxygen scavenger, and moreparticularly to an oxygen scavenger which can effectively removedissolved oxygen in water and, in particular, is useful in inhibitingthe corrosion in a boiler system by removing dissolved oxygen in feedwater. In addition, the present invention relates to boiler watertreatment chemical including such an oxygen scavenger and descalingchemicals.

[0003] Dissolved oxygen in feed water contributes corrosion incomponents of a boiler system, such as a boiler main body, a heatexchanger and an economizer arranged in an upstream of the boiler mainbody, and a steam and condensate piping arranged in a downstream of theboiler main body. To inhibit the corrosion in the boiler system,dissolved oxygen in feed water should be removed by deoxidizingtreatment of the feed water of the boiler.

[0004] Conventionally, chemical treatment or physical treatment has beenapplied for the removal of dissolved oxygen. As for the chemicaltreatment, a method of adding an oxygen scavenger such as hydrazine(N2H4), sodium sulfite (Na2SO3), hydroxylamine group, or saccharide intothe boiler water has been widely employed. Proposed in JPB S59-42073 andJPA H6-23394 is an agent containing hydroxylamine group and neutralamine.

[0005] However, the safety for humans of hydrazine is doubtful and thusthe handling of hydrazine is at stake.

[0006] Since the reaction between sodium sulfite and oxygen is toorapid, sodium sulfite dissolved in water and stored in a tank reactswith oxygen in air before it is added in feed water, thereby reducingthe concentration of effective component thereof. Therefore, there is aproblem that sodium sulfite sometimes does not produce sufficient effectof dissolved oxygen removal. Since the feed water treated with sodiumsulfite contains sulphate ion as a reaction product of the sodiumsulfite and oxygen, there is another problem that the corrosion andscale in a boiler system are easily caused.

[0007] There is also a problem that hydroxylamine group generates acidsuch as nitric acid when the hydroxylamine group is added in feed waterand reacts with oxygen in the boiler, thereby reducing corrosioninhibition effect for the boiler main body.

[0008] Saccharide has disadvantages in that it is difficult to measurethe residual concentration in boiler water and thus difficult to controlthe right amount to be added, and saccharide gives odor to the steam.

[0009] Using azo compound as an oxygen scavenger has been alreadyproposed. For example, 2,2-azobis (N,N′-dimethlene isobuthy amidine)2,2-azobis (isobuthyl amide)üE2 hydrate, 4,4-azobis (4-cyano caproicacid), and 2,2-azobis (2-amidino propane)üEHCI have been proposed.

[0010] Each of these azo compounds provides high efficiency of dissolvedoxygen removal. However, azo compounds have disadvantages in producingvarious organic matters such as formic acid and acetic acid in a boilerdrum and the steam and thereby adversely affecting the steam quality andthe steam purity.

SUMMARY OF THE INVENTION

[0011] It is the first object of the present invention to provide anovel oxygen scavenger which can efficiently remove dissolve oxygen inboiler feed water while providing high safety for humans.

[0012] It is the second object of the present invention to provide anoxygen scavenger having a heterocyclic compound with N-substituted aminogroup as an effective component which can adequately exhibit thedeoxidization effect not only for feed water lines, a boiler main body,or steam and condensate lines for high temperature water, but also forfeed water lines for low temperature water.

[0013] It is the third object of the present invention to provide anovel chemical for treating boiler water which can exhibit corrosioninhibition effect to both a boiler main body and a piping for the steamand condensate.

[0014] It is the fourth object of the present invention to provide aboiler water treatment chemical which has high corrosion inhibitioneffect by a heterocyclic compound with N-substituted amino group andexhibit excellent corrosion inhibition effect and scale inhibitioneffect as a state of a solution which contains component agents.

[0015] In an oxygen scavenger of a first aspect, the effective componentthereof consists essentially of a heterocyclic compound having N-N bondin a ring thereof.

[0016] In an oxygen scavenger of a second aspect, the effectivecomponent thereof consists of a heterocyclic compound havingN-substituted amino group or its water soluble salt.

[0017] In an oxygen scavenger of a third aspect, the effective componentthereof consists of the following heterocyclic compound:

[0018] (wherein a, b are integers between 0 and 5 to satisfy a relation“2≦a+b≦5”).

[0019] In an oxygen scavenger of a fourth aspect, the effectivecomponent thereof consists essentially of a heterocyclic compoundrepresented by the following formula:

[0020] (wherein R₁, R₂, R₃, R₄ may be the same or different from eachother and each designates any one of hydrogen, lower alkyl group having1-8 carbon atoms, and aryl group also having 1-8 carbon atoms, and Xdesignates any one of hydrogen, amino group, alkyl group or dialkylaminogroup having 1-8 carbon atoms, and lower alkyl group or aryl grouphaving 1-8 carbon atoms).

[0021] In an oxygen scavenger of a fifth aspect, the effective componentthereof consists essentially of azodicarbonamide.

[0022] The oxygen scavengers of the first through fifth aspect may beprepared by combining two or more kinds of components.

[0023] The amount of the effective component of each aspect is notlimited and can be altered to suitably correspond to the concentrationof dissolved oxygen in water as a subject. Normally, the amount is,however, between 0.001 and 1000 mg, preferably between 1 and 300 mgrelative to 1 lit. of feed water.

[0024] An oxygen scavenger of a sixth aspect includes a heterocycliccompound with N-substituted amino group, or the salt thereof, and ahydroxybenzene derivative.

[0025] In the oxygen scavenger of the sixth aspect, because of thecatalysis of the hydroxybenzene derivative, the heterocyclic compoundwith N-substituted amino group or the salt thereof can exhibit theexcellent deoxidization effect even in feed water lines for lowtemperature water.

[0026] A seventh aspect provides a chemical for treating boiler waterincluding a heterocyclic compound with N-substituted amino group andneutral amine.

[0027] An eighth aspect provides a boiler water treatment chemicalincluding a heterocyclic compound with N-substituted amino group, or thesalt thereof, and alkaline agent and/or water soluble polymer.

BRIEF DESCRIPTION OF THE DRAWING

[0028]FIG. 1 is a graph showing results of examples 36, 37 andcomparative examples 6 through 8; and

[0029]FIG. 2 is a graph showing results of examples 45 through 49 and acomparative example 21.

PREFERRED EMBODIMENTS

[0030] 1. First Aspect

[0031] In an oxygen scavenger of a first aspect, the effective componentthereof consists of a heterocyclic compound having N-N bond in a ringthereof. Included as such a heterocyclic compound is preferably at leastof one of the followings:

[0032] The above heterocyclic compounds may be used alone or incombination.

Examples 1 through 10

[0033] Effect of the oxygen scavenger of the first aspect has beentested as follow.

[0034] Softened water saturated with oxygen in air at the roomtemperature was fed into a steam generator test autoclave and theautoclave was operated to generate steam under the following conditions:

[0035] Temperature: 185° C., Pressure: 1 MPa, Amount of Evaporation: 12liters/hr, and Blow Rate: 10%.

[0036] The generated steam was completely condensed to produce condensedwater. Then, the dissolved oxygen concentration in the condensed waterwas measured by a dissolved oxygen meter. Thus obtained value was usedas data of a comparative example 1.

[0037] On the other hand, steam was generated under the same conditionsexcept that the oxygen scavenger was added in the feed water. Then, thedissolved oxygen concentration in the condensed water of the steam wasalso measured. The difference between thus obtained value and the dataof the comparative example 1 was calculated as an amount of extractionand the ratio of the extraction to the data of the comparative examplewas calculated as an extraction ratio (%).

[0038] As for each example 1 through 10, the heterocyclic compound shownin Table 1 was dissolved in the aforementioned softened water to prepareaqueous solution with a predetermined concentration, then the aqueoussolution was fed into the feed water by a fixed displacement pump, andthe concentration of the heterocyclic compound to the feed water wascontrolled to be as shown in Table 1.

[0039] The results are shown in Table 1. TABLE 1 Concentration ofHeterocyclic compound dissolved oxygen Concentration in in flocculatedAmount of removal Rate of removal Kind feed water (mg/L) water (mg/L)(mg/L) (%) Example 1 1,3-dimethyl-5-pyrazolone 45 2.00 6.25 75.8 Example2 1,3-dimethyl-5-pyrazolone 80 0.50 7.75 93.9 Example 3 urazol 20 3.604.65 50.4 Example 4 urazol 40 0.50 7.75 93.9 Example 5 6-azauracil 452.35 5.90 71.5 Example 6 6-azauracil 90 0.40 7.85 95.2 Example 73-methyl-5-pyrazolone 40 1.75 6.50 78.8 Example 8 3-methyl-5-pyrazolone80 0.35 7.90 95.8 Example 9 3-methyl-5-pyrazoline-5-on 40 1.75 6.50 78.8Example 10 3-methyl-5-pyrazoline-5-on 80 0.40 7.85 95.2 Comparative None 0 8.25 — — Example 1

[0040] 2. Second Aspect

[0041] In an oxygen scavenger of a second aspect, the effectivecomponent thereof consists of a heterocyclic compound havingN-substituted amino group or water soluble salt thereof. Included assuch a heterocyclic compound is preferably at least one of thefollowings:

[0042] As the salt thereof, for example, water soluble salt of theaforementioned heterocyclic compounds and aliphatic carboxylic acid suchas succinic acid, glutaric acid, adipic acid, gluconic acid, glycollicacid, lactic acid, malic acid, tartaric acid, or citric acid, orpolycarboxylic acid such as polyacrylic acid is preferably employed, butthe salt thereof is not limited thereto.

[0043] The above heterocyclic compounds or the salts thereof may be usedalone or in combination.

Examples 11 through 21

[0044] The deoxidizing treatment was made in each example in the samemanner as the above examples 1 through 10 except using the heterocycliccompound shown in Table 2 as the effective component of the oxygenscavenger to have the concentration of the heterocyclic compound in thefeed water as shown in Table 2. The results are shown in Table 2. TABLE2 Concentration of Heterocyclic compound dissolved oxygen Concentrationin in flocculated Amount of removal Rate of removal Kind feed water(mg/L) water (mg/L) (mg/L) (%) Example 11 N-aminomorpholine 25 1.60 6.6580.1 Example 12 N-aminomorpholine 50 0.45 7.80 94.5 Example 13N-aminomorpholine 85 0.35 7.90 95.8 Example 141-amino-4-methylpiperazine 40 1.10 7.15 86.7 Example 151-amino-4-methylpiperazine 80 0.40 7.85 95.2 Example 16N-aminohomopiperidine 40 1.20 7.05 85.5 Example 17 N-aminohomopiperidine80 0.45 7.80 94.5 Example 18 1-aminopyrrolidine 40 0.95 7.35 89.1Example 19 1-aminopyrrolidine 80 0.45 7.80 94.5 Example 201-aminopiperidine 40 0.95 7.30 88.5 Example 21 1-aminopiperidine 80 0.407.85 95.2 Comparative None  0 8.25 — — Example 1

[0045] 3. Third Aspect

[0046] In an oxygen scavenger of a third aspect, the effective componentthereof consists of the following heterocyclic compound:

[0047] Included as such a heterocyclic compound are preferably at leastone of the followings:

[0048] The above heterocyclic compounds may be used alone or incombination.

Examples 22 through 27

[0049] The deoxidizing treatment was made in each example in the samemanner as the above examples 1 through 10 except using the heterocycliccompound shown in Table 3 as the effective component of the oxygenscavenger to have the concentration of the heterocyclic compound asshown in Table 3. The results are shown in Table 3. TABLE 3Concentration of Heterocyclic compound dissolved oxygen Concentration inin flocculated Amount of removal Rate of removal Kind feed water (mg/L)water (mg/L) (mg/L) (%) Example 22 2,3-diaminopyridine 250 3.60 4.6556.4 Example 23 2,3-diaminopyridine 400 2.15 6.10 73.9 Example 242-amino-3-hydroxypyridine  40 2.35 5.90 71.5 Example 252-amino-3-hydroxypyridine  55 0.75 7.50 90.9 Example 262-amino-3-hydroxypyridine  65 0.50 7.75 93.9 Example 272-amino-3-hydroxypyridine 140 0.10 8.15 98.8 Comparative None  0 8.25 —— Example 1

[0050] 4. Fourth Aspect

[0051] In an oxygen scavenger of a fourth aspect, the effectivecomponent thereof consists of a heterocyclic compound represented by thefollowing formula:

[0052] In this effective component of the oxygen scavenger of the lofourth aspect, for example, methyl group is preferably used as loweralkyl group having 1-8 carbon atoms designated with R₁, R₂, R₃, R₄ andphenyl group or tolyl group is preferably used as aryl group also having1-8 carbon atoms. In addition, methyl group or aminomethyl group ispreferably used as alkyl group or dialkylamino group having 1-8 carbonatoms designated with X.

[0053] Included as such a heterocyckic compound is preferably at leastone of the followings:

[0054] The above heterocyclic compounds may be used alone or incombination.

Examples 28 through 34

[0055] The deoxidizing treatment was made in each example in the samemanner as the above examples 1 through 10 except using the heterocycliccompound shown in Table 4 as the effective component of the oxygenscavenger to have the concentration of the heterocyclic compound in thefeed water as shown in Table 4. The results are shown in Table 4. TABLE4 Concentration of Heterocyclic compound dissolved oxygen Concentrationin in flocculated Amount of removal Rate of removal Kind feed water(mg/L) water (mg/L) (mg/L) (%) Example 28 5-aminouracil 30 3.00 5.2563.6 Example 29 5-aminouracil 50 1.30 6.95 84.2 Example 30 5-aminouracil90 1.10 7.15 86.7 Example 31 5,6-diamino-1,3-dimethyluracil 35 2.00 5.2563.6 Example 32 5,6-diamino-1,3-dimethyluracil 50 0.95 7.30 88.5 Example33 5,6-diamino-1,3-dimethyluracil 70 0.45 7.80 94.5 Example 345,6-diamino-1,3-dimethyluracil 100  0.35 7.90 95.8 Comparative None  08.25 — — Example 1

[0056] 5. Fifth Aspect

[0057] In an oxygen scavenger of a fifth aspect, the effective componentthereof is azodicarbonamide (NH2CON=NCONH2).

[0058] Azodicarbonamide has an advantage in maintaining the purity ofgenerated steam without changing water quality in the boiler because theazodicarbonamide does not produce any organic matter such as formic acidor acetic acid.

Example 35, Comparative Examples 2 through 5

[0059] The deoxidizing treatment was made in this example and eachcomparative example in the same manner as the above examples 1 through10 except adding the azo compound shown in Table 5 as the effectivecomponent of the oxygen scavenger to have the concentration of 150 mg/Lin the feed water. The results are shown in Table 5.

[0060] Main products in the generated steam and main products in theautoclave are analyzed, respectively. The results are also shown inTable 5. TABLE 5 Concentration of dissolved oxygen Amount of Rate of inflocculated removal removal Main product in Azo compound water (mg/L)(mg/L) (%) Main product in steam autoclave Example 35 azodicarbonamide0.35 7.90 95.8 carbon dioxide, ammonia — Comparative No added 8.25 — — —— Example 1 Comparative 2,2-azobis(N,N′- 1.05 7.20 87.3 acetone,methylamine, formic acid, acetic Example 2 dimethyleneisobuthylamidine)isopropyl alcohol acid, isopropyl alcohol Comparative2,2-azobis(isobuthylamide)·2hydrate 0.25 8.00 97.0 acetone, carbondioxide, formic acid, acetic Example 3 isopropyl alcohol, ammonia acid,isopropyl alcohol Comparative 4,4-azobis(4-cyanocaproic acid) 0.35 7.9095.8 carbon dioxide various organic acid Example 4 Comparative2,2-azobis(2-amidino propane)HCl 0.45 7.85 95.2 acetone, isopropylalcohol, formic acid, isopropyl Example 5 ammonia alcohol

[0061] As apparent from Table 5, all of the azo compounds provide highrates of dissolved oxygen removal. In particular, azodicarbonamidegenerates no organic acid changing the water quality of the feed waterin the autoclave which corresponds to a boiler drum so thatazodicarbonamide is preferably used as oxygen scavenger for feed waterof the boiler.

[0062] 6. Sixth Aspect

[0063] An oxygen scavenger of a sixth aspect includes a heterocycliccompound with N-substituted amino group, or the salt thereof, and ahydroxybenzene derivative.

[0064] In the oxygen scavenger of the sixth aspect, because of thecatalysis of the hydroxybenzene derivative, the heterocyclic compoundwith N-substituted amino group or the salt thereof can exhibit theexcellent deoxidization effect even in feed water lines for lowtemperature water.

[0065] The heterocyclic compound with N-substituted amino group ispreferably at least one of 1-aminopyrrolidine,1-amino-4-methlpiperazine, 1-aminopiperidine, 1-aminohomopiperidine,1,4-diaminopiperazine, N-aminomorholine, and morholinobyguanide. As thesalt thereof, for example, water soluble salt of the aforementionedheterocyclic compounds and carboxylic acid such as succinic acid,gluconic acid, glutaric acid, adipic acid, glycollic acid, lactic acid,malic acid, tartaric acid or citric acid or polycarboxylic acid such aspolyacrylic acid is preferably employed, but the salt thereof is notlimited thereto. These heterocyclic compounds and the salts thereof maybe suitably used alone or in combination.

[0066] As the hydroxybenzene derivative, hydroquinone,2,3-dimethyl-1,4-hydroquinone, catechole, 4-tert-buthyl catechol,pyrogallol, 1,2,4-hydroxybenzene, gallic acid, 2-aminophenol,2,4-diaminophenol,4-aminophenol may be employed, but the hydroxybenzenederivative is not limited to these. The hydroxybenzene derivative mayalso be suitably used alone or in combination.

[0067] Though the oxygen scavenger of the sixth aspect can be preparedby mixing the heterocyclic compound with N-substituted amino group orthe salt thereof and the hydroxybenzene derivative, these may beseparately injected.

[0068] The amount of the oxygen scavenger of the sixth aspect can bealtered to suitably correspond to the concentration of dissolved oxygenand other water conditions in feed water of a boiler system as asubject. Normally, the heterocyclic compound with N-substituted aminogroup or the salt thereof and the hydroxybenzene derivative are,however, each added by between 0.001 and 1000 mg, preferably between0.01 and 300 mg, more preferably between 0.02 and 100 mg relative to 1lit. of feed water.

[0069] The effect ratio of the heterocyclic compound with N-substitutedamino group or the salt thereof and the hydroxybenzene derivative in theoxygen scavenger of the sixth aspect is heterocyclic compound withN-substituted amino group or salt thereof hydroxybenzene derivative=1 :0.001-10 (ratio in weight). When the hydroxybenzene derivative is lessthan the ratio, the effect improved by using the hydroxybenzenederivative according to the present invention, i.e. the improved effectof the deoxidization to low temperature water can not be sufficientlyprovided. On the other hand, when the hydroxybenzene derivative is morethan the ratio, the treatment cost becomes higher relative to theincrease in the effect.

[0070] The oxygen scavenger of the sixth aspect is dissolved in water insuch a manner that the acescent hydroxybenzene derivative is neutralizedby the heterocyclic compound having basic N-substituted amino group.When it is difficult to dissolve the oxygen scavenger, adding alkalisuch as caustic soda (NaOH) improves the solubility of the oxygenscavenger.

[0071] Though the oxygen scavenger of the sixth aspect includes theheterocyclic compound with N-substituted amino group or the salt thereofand the hydroxybenzene derivative if necessary, another oxygen scavengeror corrosion inhibitor such as hydrazine, sodium sulfite, succinic acidor gluconic acid or furthermore dispersant, chelate compound, descalingchemicals, or the mixture of some among these may also be added.

[0072] The oxygen scavenger of the sixth aspect can be effectively usedin boiler systems of various types such as low pressure, mediumpressure, and high pressure boiler systems and is not restricted at allby the boiler pressure, the boiler type, or the kind of feed water.

Examples 36, 37, Comparative Examples 6 through 8

[0073] After filling 1 lit. of softened water of Atsugi-city's tap waterinto an Erlenmeyer flask and controlling pH to be 9.0 by using NaOH, itwas agitated two hours in a constant-temperature water bath at 60° C. insuch a manner as to be saturated by oxygen in air. The concentration ofdissolved oxygen at this point was measured by a dissolved oxygen meter(“MOCA3600” manufactured by Obisfair Co., Ltd.) with the result that itwas 4.75 mg/L.

[0074] After adding chemicals by the respective amounts shown in Table 6into the water in the Erlenmeyer flask and sufficiently agitating them,the resultant solution was poured into three furan bottles of 200 mlcapacity and the furan bottles were capped without space therein andthen returned into the constant-temperature water bath at 60° C. tocause the reaction of the solution. The furan bottles were taken outfrom the constant-temperature water bath one at a time with the passageof predetermined periods (5, 10, 20 minutes) and the concentrations ofdissolved oxygen in the solution were measured by the dissolved oxygenmeter. The residual rate of dissolved oxygen in each sample solution wascalculated from the ratio of the concentration of dissolved oxygen afteradding the chemicals to that before adding the chemicals. Theseoperations were rapidly performed in nitrogen-atmosphere.

[0075] The results are shown in Table 6 and FIG. 1.

[0076] As apparent from the results, it is found that the deoxidizationreaction is significantly speeded up by using hydroquinone (HQ) as ahydroxybenzene derivative with 1-aminopyrrolidine (APY) or1-amino-4-methylpiperazine (AMPI) as a heterocyclic compound withN-substituted amino group. TABLE 6 Concentration of dissolved oxygenAgent added after addition of agent (mg/L) and its concentration Just(mg/L) after 5 min. 10 min. 20 min. Ex. APY AMP I HQ addition laterlater later Ex. 36 100 — 2 4.75 0.78 0.18 0.08 37 — 100 2 4.75 2.01 0.960.58 Co.  6 100 — — 4.75 3.69 3.33 3.12  7 — 100 — 4.75 3.86 3.63 3.52 8 — — 2 4.75 4.43 4.33 4.31

[0077] 7. Seventh Aspect

[0078] A seventh aspect provides a chemical for treating boiler waterincluding a heterocyclic compound with N-substituted amino group andneutral amine.

[0079] The essential components of the chemical of this aspect are theheterocyclic compound with N-substituted amino group and the neutralamine.

[0080] The heterocyclic compound with N-substituted amino group exhibitsthe excellent deoxidization effect by reacting with dissolved oxygen inboiler water so as to inhibit the corrosion in a boiler main body.

[0081] The chemical has the following useful functions in addition tothe aforementioned functions of the heterocyclic compound withN-substituted amino group.

[0082] The heterocyclic compound with N-substituted amino group hasvolatility characteristics and excellent reduction ability relative toiron. In other words, the heterocyclic compound has functions ofinhibiting the oxidation of iron, that is, inhibiting the corrosion ofiron.

[0083] Therefore, steam condensate generated from boiler water treatedwith the chemical of the seventh aspect is deprived of thecharacteristics of corroding a piping through which the steam condensatepasses because of the aforementioned functions of the heterocycliccompound which is included in the steam condensate. In addition, thesteam condensate is held in a pH range of neutral or alkaline because ofthe functions of the neutral amine which is also included in thecondensate, thereby inhibiting the corrosion of the piping through whichthe condensate passes.

[0084] That is, the chemicals of this aspect can exhibit the corrosioninhibition effect in both the boiler main body and the steam andcondensate piping.

[0085] Any compound which can exhibit the functions and effects asmentioned above may be employed as the heterocyclic compound withN-substituted amino group. For example, N-aminomorpholine,1-aminopyrrolidine, 1-amino-4-methylpiperazine, 1,4-diaminopiperazine,1-aminopiperidine, 1-aminohomopiperidine, morpholinobiguamide may bepreferably employed and water soluble salt of the aforementionedheterocyclic compounds and carboxylic acid such as succinic acid,gluconic acid, glutaric acid, adipic acid, glycollic acid, lactic acid,malic acid, tartaric acid or citric acid, polycarboxylic acid such aspolyacrylic acid are also preferably employed. Moreover, theseheterocyclic compounds and the salts thereof may be suitably used aloneor in combination.

[0086] Any compound capable of making the boiler water after treatmentand the steam condensate neutral or alkaline may be employed as theneutral amine, the other essential component of the chemical. Forexample, cyclohexylamine, 2-amino-2-methyl-1-propanol, monoethanolamine,diethanolamine, morpholine, monoisopropanolamine, diethylethanolamine,dimethylpropanolamine, dimethylethanolamine, and dimethylpropylamine maybe preferably employed. These may be suitably used alone or incombination.

[0087] The chemical of the seventh aspect is prepared by mixing theheterocyclic compounds and the neutral amine as mentioned above.

[0088] The mixing ratio thereof can be determined to suitably correspondto the concentration of dissolved oxygen and other water conditions infeed water of a boiler system as a subject. However, the heterocycliccompounds and the neutral amine are normally each added by between 0.001and 1000 mg, preferably between 0.01 and 300 mg, more preferably between0.02 and 100 mg relative to 1 lit. of feed water.

[0089] Though the essential components of the chemical of the seventhaspect are the heterocyclic compound with N-substituted amino group andthe neutral amine, another known oxygen scavenger or corrosion inhibitorsuch as hydrazine, sodium sulfite, succinic acid or gluconic acid orfurthermore the known dispersant, chelate compound, descaling chemicals,or the mixture of some among these may also be added.

[0090] The chemical of the seventh aspect can be effectively used inboiler systems of various types such as low pressure, medium pressure,and high pressure boiler systems and is not restricted at all by theboiler pressure or the type of feed water.

Examples 38 through 44, Comparative Examples 9 through 20

[0091] After feeding softened water of Atsugi-city's tap water which hasbeen saturated by oxygen in air at 40° C. into an experimental electricboiler with a capacity of 5 liters and the boiler was operated togenerate steam under the following conditions:

[0092] Temperature: 183° C., Pressure: 1 MPa, Amount of Evaporation: 12liters/hr, and Blow Rate: 10%.

[0093] The steam was cooled to produce condensate. The condensate wascooled to 50° C. and then fed into a column. Previously disposed in thecolumn and the aforementioned experimental electric boiler were testpieces made of steel (SS400 of Japanese Industrial Standard) each havinga length of 50 mm, a width of 15 mm, and a thickness of 1 mm. The testpieces were dipped in said condensate 96 hours.

[0094] The amounts of corrosion of the respective pieces were measuredto calculate the corrosion rates in the boiler water and the condensate.The resultant values were indexes representing the degree of corrosionof the pieces caused by the boiler water without chemical treatment. Theresults are shown in Table 8 as a comparative example 9.

[0095] It should be noted that the concentration of nitrate ion and theconcentration of nitrite ion in the boiler water after the operationwere measured and the results are also shown in Table 8.

[0096] The chemical components shown in Table 7 were dissolved insoftened water mentioned above in such a manner as to have therespective indicated concentrations in the softened water and thensupplied to the boiler by using a fixed displacement pump. TABLE 7Concentration of each component (mg/L) Heterocyclic compound Neutralamine Hydroxylamine group 1-amino 2-amino-2- diethylhyd isoproxylhydN-amino 1-amino -4-methyl cyclohexyl methyl-1- monoethanol -roxylamine-roxylamine -morpholine -pyrrolidine -piperazine -amine propanol -amineComparative Example 10 36 — — — — — — — Comparative Example 11 — 36 — —— — — — Comparative Example 12 36 — — — — 30 — — Comparative Example 1336 — — — — — 30 — Comparative Example 14 36 — — — — — — 30 ComparativeExample 15 — 36 — — — 30 — — Comparative Example 16 — 36 — — — — 30 —Comparative Example 17 18 18 — — — 30 — — Comparative Example 18 — — 36— — — — — Comparative Example 19 — — — 36 — — — — Comparative Example 20— — — — 36 — — — Example 38 — — 36 — — 30 — — Example 39 — — 36 — — — 30— Example 40 — — 36 — — — — 30 Example 41 — — — 36 — 30 — — Example 42 —— — 36 — — 30 — Example 43 — — — — 36 30 — — Example 44 — — — — 36 — 30—

[0097] As for condensate of steam generated from the softened water inwhich the chemical components are dissolved, the corrosion test was madeunder the same conditions as that of the aforementioned comparativeexample 9 to calculate the corrosion rate of test coupons.

[0098] In addition, the concentration of nitrate ion and theconcentration of nitrite ion in the boiler water after the operationwere measured. The results are shown in Table 8. TABLE 8 Corrosion rateof test piece (mdd) Concentration of nitric ion and nitrite In boiler Incondensed ion in boiler water water water nitric ion nitrite ionComparative Example 9 10.5  143.5 not detected not detected ComparativeExample 10 2.0 48.3 2.3 3.1 Comparative Example 11 2.3 39.4 3.5 4.2Comparative Example 12 2.0 29.2 2.8 3.6 Comparative Example 13 1.8 34.62.7 2.9 Comparative Example 14 1.7 33.3 1.9 3.3 Comparative Example 152.4 26.4 4.3 4.1 Comparative Example 16 2.6 28.6 5.2 4.5 ComparativeExample 17 2.1 24.3 3.4 3.8 Comparative Example 18 1.0 30.3 not detectednot detected Comparative Example 19 1.2 23.5 not detected not detectedComparative Example 20 0.9 21.6 not detected not detected Example 38 0.88.4 not detected not detected Example 39 1.0 9.3 not detected notdetected Example 40 0.7 9.1 not detected not detected Example 41 1.1 9.5not detected not detected Example 42 0.9 9.8 not detected not detectedExample 43 0.8 11.3 not detected not detected Example 44 1.0 12.5 notdetected not detected

[0099] As apparent from Table 7 and Table 8, the following facts arefound.

[0100] 1) The chemicals including hydroxyamine groups (comparativeexamples 10 through 17) are not convenient for inhibiting the corrosionof the boiler because nitrate ion and nitrite ion are produced in theboiler water.

[0101] 2) Using the heterocyclic compound with N-substituted amino groupalone reduces the corrosion rate of iron in the boiler water and doesnot produce nitrate ion and nitrite ion in the boiler water. Since,however, the corrosion rate of iron in the condensate is still large sothat the corrosion in the steam and condensate piping will be caused,the heterocyclic compound is not convenient.

[0102] 3) As compared to the above comparative examples, using any oneof the chemicals of the examples does not produce nitrate ion andnitrite ion in the boiler water and significantly inhibits the corrosionof iron in both the boiler water and the condensate.

[0103] 8. Eighth Aspect

[0104] A boiler water treatment chemical of an eighth aspect includes aheterocyclic compound with N-substituted amino group, or the saltthereof, and alkalic agent and/or water soluble polymer.

[0105] The heterocyclic compound with N-substituted amino group or thesalt thereof has features of slower deoxidization reaction under theneutral condition and of higher deoxidization reaction under thealkaline condition in the case of low temperature water. Accordingly,using the alkalic agent improves the deoxidization effect of theheterocyclic compound even in the pipeline for low temperature water. Asa result of this, the deoxidization effect in the feed water lines isfurther improved and the amount of iron entered into the boiler isreduced. Iron entered from the feed water and iron eluted from theboiler drum adhere as iron oxide sludge to a heating surface. The ironoxide sludge causes an oxygen concentration cell or the like so as tocontribute the corrosion. The increase in the corrosion inhibitioneffect in the feed water line can reduce such a secondary corrosion.

[0106] Using the water soluble polymer reduces the corrosion, caused bythe iron oxide sludge, by its sludge dispersing function and,furthermore, can prevent the scaling on the heating surface even whenthe hardness components leak from a softener or ion exchange equipment.

[0107] Since pH of the steam condensate is held to be neutral oralkaline by using the neutral amine, the corrosion of the pipeline forthe steam condensate (i.e. the steam drain line) is inhibited.

[0108] As the heterocyclic compound with N-substituted amino group usedin the eighth aspect, 1-aminopyrrolidine, 1-amino-4-methlpiperazine,1-aminopiperidine, 1-aminohomopiperidine, 1,4-diaminopiperazine,N-aminomorpholine, and morpholinobyguanide are preferably employed. Asthe salt thereof, for example, water soluble salt of the aforementionedheterocyclic compounds and aliphatic carboxylic acid such as succinicacid, glutaric acid, adipic acid, gluconic acid, glycollic acid, lacticacid, malic acid, tartaric acid, or citric acid, or polycarboxylic acidsuch as polyacrylic acid is preferably employed, but the salt thereof isnot limited thereto. These heterocyclic compounds and the salts thereofmay be suitably used alone or in combination.

[0109] As the alkaline agent used in the eighth aspect, sodiumhydroxide, potassium hydroxide, sodium carbonate, and potassiumcarbonate are preferably employed, but it is not limited thereto. Thesealkaline agents may be suitably used alone or in combination.

[0110] As the water soluble polymer used in the eighth aspect,polyacrylic acid, polymaleic acid, polymethacrylate acid, copolymer ofacrylic acid and acrylic amide, copolymer of acrylic acid andhydroxyallyloxypropanesulfonic acid, copolymer of acrylic acid and2-acrylamide-2-methylpropanesulfonic acid, and the salt thereof arepreferably employed, but it is not limited thereto. These water solublepolymers may be suitably used alone or in combination.

[0111] As the neutral amine used in the eighth aspect, any compoundcapable of making the boiler water and the steam condensate neutral oralkaline may be employed. For example, cyclohexylamine,2-amino-2-methyl-1-propanol, monoethanolamine, diethanolamine,morpholine, monoisopropanolamine, dimethylethanolamine,diethylethanolamine, dimethylpropanolamine, and dimethylpropilamine maybe preferably employed. These may be suitably used alone or incombination.

[0112] Though the boiler water treatment chemical of the eighth aspectcan be prepared by mixing the aforementioned heterocyclic compound withN-substituted amino group or the salt thereof and the alkalic agentand/or water soluble polymer, and further by mixing the neutral amine ifnecessary, these may be separately injected.

[0113] The amount of the boiler water treatment chemical of the eighthaspect can be altered to suitably correspond to the concentration ofdissolved oxygen and other water conditions in feed water of a boilersystem as a subject. However, the heterocyclic compound withN-substituted amino group or the salt thereof and the alkalic agentand/or water soluble polymer are normally each added by between 0.001and 1000 mg, preferably between 0.01 and 300 mg, more preferably between0.02 and 100 mg relative to 1 lit. of feed water.

[0114] Particularly, the alkaline agent is preferably added in such amanner that pH becomes between 8 and 12, depending on the type of aboiler.

[0115] When the neutral amine is used with the boiler water treatmentchemical, the preferable amount of the neutral amine is between 0.01 and500 mg, particularly between 0.1 and 100 mg relative to 1 lit. of feedwater.

[0116] In the boiler water treatment chemical of the eighth aspect, theratio of the heterocyclic compound with N-substituted amino group or thesalt thereof and the alkaline agent and/or water soluble polymer ispreferably set as follows (the ratio is in weight).

[0117] (1) When the heterocyclic compound with N-substituted amino groupor the salt thereof and the alkalic agent are used together,

[0118] Heterocyclic compound with N-substituted amino group or Saltthereof: Alkaline agent=1:0.01-20.

[0119] (2) When heterocyclic compound with N-substituted amino group orthe salt thereof and the water soluble polymer are used together,

[0120] Heterocyclic compound with N-substituted amino group or Saltthereof: Water soluble polymer=1:0.01-20.

[0121] (3) When heterocyclic compound with N-substituted amino group orthe salt thereof and the alkaline agent and the water soluble polymerare used together,

[0122] Heterocyclic compound with N-substituted amino group or Saltthereof: Alkaline agent: Water soluble polymer=1:0.01-20:0.01-20.

[0123] Moreover when the neutral amine is used therewith, the preferableratio is Heterocyclic compound with N-substituted amino group or Saltthereof: Neutral amine=1:0.01-20 (ratio in weight).

[0124] Though the essential components of the boiler water treatmentchemical of the eighth aspect are the heterocyclic compound withN-substituted amino group or the salt thereof and the alkaline agentand/or the water soluble polymer and the neutral amine if necessary,another known oxygen scavenger or corrosion inhibitor such as hydrazine,sodium sulfite, saccharide, succinic acid, gluconic acid or amines otherthan the aforementioned neutral amine, or furthermore the knowndispersant, chelate compound, descaling chemicals, or the mixture ofsome among these may also be added.

[0125] The boiler water treatment chemical of the eighth aspect can beeffectively used in boiler systems of various types such as lowpressure, medium pressure, and high pressure boiler systems and is notrestricted at all by the boiler pressure, the boiler type, or the typeof feed water.

[0126] Hereinafter, the eighth aspect will be described in more detailwith some examples and comparative examples.

Examples 45 through 49, Comparative example 21

[0127] Five kinds of testing liquids were prepared by adding sodiumhydroxide as the alkaline agent into 1 lit. of deionized water in such amanner that respective pHs become 8.0, 9.0, 10.0, 11.0, and 12.0. Thesewere agitated one hours in a constant-temperature water bath at 60° C.and saturated by oxygen in air. The respective concentrations ofdissolved oxygen were measured by a dissolved oxygen meter (“MOCA3600”manufactured by Obisfair). After adding 100 mg of 1-aminopyrrolidine(1-AP) as the heterocyclic compound with N-substituted amino group andsufficiently agitating them, the resultant solutions were poured intofuran bottles of 200 ml capacity and the furan bottles were cappedwithout space therein and then returned into the constant-temperaturewater bath at 60° C. to cause the reaction of the solution. After 20minutes, the furan bottles were taken out from the constant-temperaturewater bath and the concentrations of dissolved oxygen in the solutionwere measured by the dissolved oxygen meter. The residual rate ofdissolved oxygen in each testing liquid was calculated from the ratio ofthe concentration of dissolved oxygen after adding the1-aminopyrrolidine to that before adding the agent (Examples 45 25through 49). These operations were rapidly performed innitrogen-atmosphere.

[0128] For comparison, the test was made for a testing liquid with 6.8pH without adding sodium hydroxide in the same manner (ComparativeExample 21).

[0129] The results of this test are shown in Table 9 and FIG. 2.

[0130] As apparent from the results, it is found that using1-aminopyrrolidine as the heterocyclic compound with N-substituted aminogroup and the alkalic agent significantly improves the deoxidizationeffect. TABLE 9 Concentration Concentration of dissolved of dissolvedRemoval oxygen before oxygen after rate of pH of test addding 1-APadding 1-AP dissolved Example water (mg/L) (mg/L) oxygen (%) Example 45 8.0 4.30 3.55 17.4 Example 46  9.0 4.30 2.65 38.4 Example 47 10.0 4.301.60 62.8 Example 48 11.0 4.30 1.00 76.7 Example 49 12.0 4.30 0.70 83.7Comparative  6.8 4.30 4.05  5.8 Example 21

Examples 50 through 55, Comparative Examples 22, 23

[0131] After adding 30 mg of 1- aminopyrrolidine as the heterocycliccompound with N-substituted amino group into softened water ofAtsugi-city's tap water which has been saturated by oxygen in air at 40°C., the resultant water were fed into an experimental electric boilerwith a capacity of 5 liters and the boiler was operated to generatesteam under the following conditions. The operating time was 240 hours.

[0132] Conditions:

[0133] Temperature: 183° C.,

[0134] Pressure: 1 MPa,

[0135] Amount of Evaporation: 11 liters/hr,

[0136] Blow Rate: 10%, and

[0137] Concentration of iron in feed water: 0.5 mg/L.

[0138] Previously disposed in the feed water line, the drum of theelectric boiler, and the steam drain line were test pieces made of steel(SS400 of Japanese Industrial Standard) each having a length of 50 mm, awidth of 15 mm, and a thickness of 1 mm. The degrees of corrosion oftest pieces were measured to calculate the corrosion ratios. The resultsare shown in Table 10. The amount of iron contained in iron oxide builtup (the amount of deposited iron) on the piece disposed in the boilerdrum was measured and the result was shown in Table 10 (ComparativeExample 22).

[0139] The chemical components shown in Table 10 were dissolved insoftened water mentioned above in such a manner as to have therespective indicated concentrations in the softened water shown in Table10 and then fed to the boiler by using a fixed displacement pump.

[0140] As for condensate of steam generated from the softened water inwhich the chemical components are dissolved, the corrosion test was madeunder the same conditions as mentioned above to calculate the corrosionrate of test pieces and the amount of deposited iron and the resultswere shown in Table 10 (Examples 50 through 55, Comparative Example 23).

[0141] As apparent from Table 10, it is found that improved corrosioninhibition effect and descaling effect can be obtained by using1-aminopyrrolidine and the alkaline agent and or the water solublepolymer, and further using the neutral amine. TABLE 10 Chemicals and itsadding rate (mg/L) Iron scale formed Water Corrosion rate (mdd) on innersurface of soluble Steam dram boiler dram Example 1·AP NaOH polymer AMPFeed line In boiler dram line (mg/cm²) Example 50 80 5 0 0 20.5 4.1 11.30.181 Example 51 30 0 5 0 36.8 4.7 12.7 0.118 Example 52 30 5 5 0 18.82.8 13.1 0.104 Example 53 30 5 0 15  17.6 3.9 4.9 0.173 Example 54 30 05 15  36.9 4.2 5.8 0.107 Example 55 30 5 5 15  18.2 2.6 5.3 0.097Comparative  0 0 0 0 81.5 20.3 63.2 0.302 Example 22 Comparative 30 0 00 37.2 7.3 12.2 0.221 Example 23

[0142] As apparent from the above description, any one of the oxygenscavengers of the first through fifth aspects of the present inventioncan efficiently remove dissolved oxygen in water. When these are used asan oxygen scavenger for feed water of a boiler, any one of these caninhibit the corrosion on a boiler main body and a steam and condensatepiping caused by dissolved oxygen. Therefore, each oxygen scavenger hasquite high industrial utility.

[0143] Further, the fifth aspect provides an oxygen scavenger whichprevents the development of by-product in the boiler so as not to affectthe purity of steam.

[0144] The sixth aspect provides an oxygen scavenger having improveddeoxidization effect in feed water lines for low temperature water andwhich is remarkably superior in corrosion inhibition in a feed waterpiping as compared with a conventional one.

[0145] The chemical for treating boiler water of the seventh aspectexhibits excellent corrosion inhibition effect relative to any of aboiler main body and steam and condensate lines although the chemical isone-component agent. This is because the heterocyclic compounds withN-substituted amino group and the neutral amine are contained in thechemical.

[0146] The eighth aspect provides a boiler water treatment chemicalhaving both the excellent corrosion inhibition effect and the descalingeffect although the chemical is one-component agent.

What is claimed is:
 1. A boiler water treatment chemical including aheterocyclic compound with N-substituted amino group, or the saltthereof, and alkalic agent and/or water soluble polymer.
 2. A boilerwater treatment chemical according to claim 1, further including neutralamine.
 3. A boiler water treatment chemical according to claim 1,wherein the heterocyclic compound with N-substituted amino group is1-aminopyrrolidine, 1-amino-4-methylpiperazine, 1-aminopiperidine,1-aminohomopiperidine,1,4-diaminopiperazine, N-aminomorpholine, ormorpholinobyguanide, and wherein the salt thereof is water soluble saltof said heterocyclic compounds and aliphatic carboxylic acid such assuccinic acid, glutaric acid, adipic acid, gluconic acid, glycollicacid, lactic acid, malic acid, tartaric acid, or citric acid, orpolycarboxylic acid such as polyacrylic acid.
 4. A boiler watertreatment chemical according to claim 1, wherein the alkalic agent issodium hydroxide, potassium hydroxide, sodium carbonate, or potassiumcarbonate.
 5. A boiler water treatment chemical according to claim 1,wherein the water soluble polymer is polyacrylic acid, polymaleic acid,polymethacrylate acid, copolymer of acrylic acid and acrylic amide,copolymer of acrylic acid and hydroxyallyloxypropanesulfonic acid,copolymer of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid,or the salt thereof.
 6. A boiler water treatment chemical according toclaim 2, wherein the neutral amine is one or more among cyclohexylamine,2-amino-2-methyl-1-propanole, monoethanolamine, diethanolamine,morpholine, monoisopropanolamine, dimethylethanolamine,diethylethanolamine, dimethylpropanolamine, and dimethylpropilamine. 7.A boiler water treatment chemical according to claim 1, wherein theratio of the heterocyclic compound with N-substituted amino group or thesalt thereof and the alkalic agent and/or water soluble polymer is setas follows in weight: i) when the heterocyclic compound withN-substituted amino group or the salt thereof and the alkalic agent areused together, heterocyclic compound with N-substituted amino group orsalt thereof: alkalic agent=1:0.01-20; ii) when the heterocycliccompound with N-substituted amino group or the salt thereof and thewater soluble polymer are used together, heterocyclic compound withN-substituted amino group or salt thereof: water solublepolymer=1:0.01-20; and iii) when the heterocyclic compound withN-substituted amino group or the salt thereof and the alkalic agent andthe water soluble polymer are used together, heterocyclic compound withN-substituted amino group or salt thereof: alkaline agent: water solublepolymer=1:0.01-20:0.01-20.
 8. A method of using an oxygen scavenger,comprising: adding to boiler water an effective amount of an oxygenscavenger including, as an effective component, a heterocyclic compoundwith N-substituted amino group, or the salt thereof, and alkaline agentand/or water soluble polymer.
 9. A method of using an oxygen scavengeraccording to claim 8, wherein said oxygen scavenger further includesneutral amine.
 10. A method of using an oxygen scavenger according toclaim 8, wherein the heterocyclic compound with N-substituted aminogroup is 1-aminopyrrolidine, 1-amino-4-methylpiperazine,1-aminopiperidine, 1-aminohomopiperidine,1,4-diaminopiperazine,N-aminomorpholine, or morpholinobyguanide, and wherein the salt thereofis water soluble salt of said heterocyclic compounds and aliphaticcarboxylic acid such as succinic acid, glutaric acid, adipic acid,gluconic acid, glycollic acid, lactic acid, malic acid, tartaric acid,or citric acid, or polycarboxylic acid such as polyacrylic acid.
 11. Amethod of using an oxygen scavenger according to claim 8, wherein thealkaline agent is sodium hydroxide, potassium hydroxide, sodiumcarbonate, or potassium carbonate.
 12. A method of using an oxygenscavenger according to claim 8, wherein the water soluble polymer ispolyacrylic acid, polymaleic acid, polymethacrylate acid, copolymer ofacrylic acid and acrylic amine, copolymer of acrylic acid andhydroxyallyloxypropanesulfonic acid, copolymer of acrylic acid and2-acrylamide-2-methylpropanesulfonic acid, or the salt thereof.
 13. Amethod of using an oxygen scavenger according to claim 9, wherein theneutral amine is one or more among cyclohexylamine,2-amino-2-methyl-1-propanole, monoethanolamine, diethanolamine,morpholine, monoisopropanolamine, dimethylethanolamine,diethylethanolamine, dimethylpropanolamine, and dimethylpropilamine. 14.A method of using an oxygen scavenger according to claim 8, wherein theratio of the heterocyclic compound with N-substituted amino group or thesalt thereof and the alkalic agent and/or water soluble polymer is setas follows in weight: i) when the heterocyclic compound withN-substituted amino group or the salt thereof and the alkalic agent areused together, heterocyclic compound with N-substituted amino group orsalt thereof: alkalic agent=1:0.01-20; ii) when the heterocycliccompound with N-substituted amino group or the salt thereof and thewater soluble polymer are used together, heterocyclic compound withN-substituted amino group or salt thereof: water solublepolymer=1:0.01-20; and iii) when the heterocyclic compound withN-substituted amino group or the salt thereof and the alkalic agent andthe water soluble polymer are used together, heterocyclic compound withN-substituted amino group or salt thereof: alkaline agent: water solublepolymer 1:0.01-20:0.01-20.